The present invention relates to a thermoplastic article. In particular, the invention pertains to a melt-processed thermoplastic film that contains a thermoplastic cellulose and a microbially-derived, renewable and biodegradable aliphatic polyester. The composition may be incorporated into a variety of products.
Because of increasing consumers' concern on environmental issues and the alleged depletion of fossil fuels, using environmentally sustainable materials in consumer products has attracted increased attention in recent decades. From an environmental sustainability standpoint, cellulose material is an attractive natural material made from abundant renewable sources ranging from wood to agricultural waste.
It is known that some cellulose derivatives can be thermally processed into various articles such as film and molded articles. However, the short carbon chain alkanoates derivatives of cellulose such as cellulose acetate and cellulose propionate have high melting temperatures making them not suitable for blending with microbial aliphatic polyester such as poly(3-hydroxybutyrate) due to its thermal decomposition at processing temperatures.
In recent years, manufacturers of plastic or thermoplastic products or materials have shown increasing interest in renewable biopolymers and cellulose-based materials as important, environmentally-friendly, natural resources. In fact, cellulose-based materials are the most abundant natural polymers that can be renewably produced each year in large quantities.
Commercially available thermoplastic cellulose derivatives are cellulose esters and ethers such as cellulose acetate (CA), cellulose acetate propionate (CAP), and cellulose acetate butyrate (CAB), methyl cellulose, ethyl cellulose, hydroxypropyl cellulose, etc. Common properties of these cellulose derivatives are that they tend to have high stiffness, low ductility, good clarity, and a narrow thermal processing window. They also have moderate heat and impact resistance. Unfortunately, the rigid and brittle nature of cellulose derivatives tends to limit their wider use in a variety of products and applications.
Native cellulose is not thermoplastic. Most cellulose esters have high melting temperatures of over 230 to 240° C. or higher, while poly(3-hydroxybutyrate) (PHB) has a melting point of 177° C. and a thermal decomposition temperature of about 200° C. Therefore most cellulose esters, even some cellulose acetate butyrate compositions having high melting points, cannot be melt blended with PHB due to decomposition of the polyhydroxyalkanoate (PHA).
To improve the performance of cellulose ester materials, blending cellulose derivatives with other polymers has been explored. The prior art blends of cellulose ester with biodegradable polymers are prepared by solution blending. Solution prepared films typically have different morphology and properties from the films of the same composition produced by melt processing. This is because melt processing cannot achieve the molecular level mixing that can be achieved in a solution blending process. However, the solution blending method is not preferred due to the use and recovery of solvents as well the corresponding environmental impact.
Thus, there is a need for environmentally sustainable films made from 100% renewable polymers. There is also a need for renewable polymers such as cellulose for sustainable plastic applications in personal hygiene and health care products. There is a further need for a film composition of cellulose and PHA with suitable melting temperatures and stability during melt processing without causing PHA to decompose. There is yet another need for melt-processed films that have suitable mechanical properties such as enhanced flexibility and ductility.